You can train by yourself in all the sites mentioned before.
Also here you can find a lot of information and theory of different resources that you can use freedom.
It’s important the practice, but also the theory.

Here you can find some books, algorithms, notes, and theory in general that you can use to prepare yourself for the ACM-ICPC. You can have all the print documents that you want in a contest, so you’re allowed to print all the material that you found useful here and use for your training or in the contests, is up to you.